THCA is found in variable quantities in fresh, undried cannabis, but is progressively decarboxylated to THC with drying, and especially under intense heating such as when cannabis is smoked[7] or cooked into cannabis edibles.

THCA is commonly used as a biomarker in drug testing along with THCV, to distinguish between prescribed synthetic Delta-9-tetrahydrocannabinol, such as Marinol, and cannabis plant material which may also be used by patients.[15]

There is also a practical legal issue of potential THC contamination of THCA which should be considered. As mentioned above, THCA decarboxylates to form THC, a Schedule I controlled substance. As such it is somewhat unlikely that any sample of THCA which may be analytically tested will not contain a quantifiable amount of THC, especially if the sampled product was retained at temperatures conducive to decarboxylation. This makes it likely that possession of THCA could get someone prosecuted for possession of THC due to contamination of the THCA with THC.